Currently, transmission systems employed in the cable television (CATV) industry provide two-way transmission of information; e.g., video, audio, multimedia and/or data; between a head end and a plurality of subscribers. Typically, the head end transmits the information destined for individual subscribers (“downstream information”) in an optical format, via one or more fiber optic links, to one or more optical nodes. Each node converts the optically-formatted downstream information into electrical signals for distribution, typically via a coaxial cable plant having a tree and branch architecture, to individual subscribers. In addition to receiving the downstream information, each individual subscriber may generate information in the form of voice, video, data, or any combination thereof, destined for the head end. The subscriber-generated information (“upstream information”) is aggregated by the coaxial cable plant and passes to the node for conversion into an optical format for transmission to the head end.
CATV service providers and their subscribers are accustomed to high reliability service. One way in which high reliability is achieved is by providing two optical paths between the head end and each optical node, one of which serves as a primary optical path and the other of which serves as a secondary or backup optical path. An optical switch switches the optical information signals from the primary path to the secondary path in the event of an unanticipated failure in the primary path. The optical switches are often located in the head end and the optical nodes.
The aforementioned optical switches generally employ an optomechanical switching component that switches between the primary path and the secondary path based on the electrical voltage that is applied to it. A portion of the optical signal in the primary and secondary paths is tapped off and converted to an electrical voltage. The voltages are monitored and if a threshold condition is violated, indicating a failure in the primary path, the switch is activated so that traffic is transferred to the secondary path. Unfortunately, the optical switch does not include any arrangement for switching back from the secondary to the primary path after the primary path has been restored. Rather, an operator or technician must perform a manual power cycle to restart the optical switches in both the head end and the optical node so that the switches return to the primary path. Restoration in this manner can be difficult because the head end and the optical node may be located 50 to 100 km apart from one another. Also, there may be many such optical switches in both the head end and the nodes, thus requiring the operator to take proper care to ensure that the correct combination of switches are power cycled so that there is no interference with traffic on the other paths.
Accordingly, it would be desirable to provide a method and apparatus for automatically restoring optical traffic from a secondary optical transmission path to a primary optical transmission path after a fault in the primary optical transmission path has been repaired without the need to perform a manual power cycle.